DE2359619C3 - Process for improving the precipitating properties of finely divided silicon dioxide - Google Patents

Description

i) V2 b ' ^s 5 parts of a hydroxylamine of the formula

ü)

2 to 25 parts formula

R ²

R ¹ —N —OH of a cyclic siloxane der

ίίί) 1 to 20 parts of a Silyl-Stiekstaff compound the formula

are treated, where R 'is a monovalent hydrocarbon radical or a halogen-substituted hydrocarbon radical, R ² , R ³ and R ^{4 are} each hydrogen, a monovalent hydrocarbon radical or a halogen-substituted monovalent hydrocarbon radical, with R ³ and R ^{4 being} a maximum of only 33 mol% hydrogen may, a has the value 1 or 2, and X

-NiI ³ Y, —ONRf or —N—

where R ^{5 is} a monovalent hydrocarbon radical or a halogen-substituted monovalent hydrocarbon radical and Y is hydrogen or R ⁵ .

It is an essential feature of this method according to the invention that the three treatment agents, the Hydroxylamine, the silyl nitrogen compound and that cyclic siloxane can be used together and at the same time come into contact with the filler. Such treatment is preferably carried out for a period of 3 to 8 hours, though can also be used for a shorter or longer period of time. Most preferred is a treatment time of 3 to 5 hours. Preferably that is Hydroxylamine diethylhydroxylamine, the cyclic siloxane hexamethyltricyclosiloxane and the silazane hexamethyldisilazane.

Instead of the trimer of the formula

(RlSiO) ₃

can also be a tetramer of the following formula (RiSiOl,

can be used.

This compound is a tetracydosiloxane, commonly known to those skilled in the art as a tetramer is. Although this tetramer can be used in the process of the invention, it is not am most preferred. The preferred cyclic siloxane is tricyclosiloxane. Although other cyclic Siloxanes can be used in the process of the invention, but they are not special useful because they do not lead to such an excellently treated filler as the aforementioned cyclic siloxanes.

Although it is not yet fully understood why using the three treating agents at the same time gives such a good treated product is, it is believed that the joint use of the three treatments becomes one catalytic effect of the type leads that the triorganosiloxy groups of the silyl nitrogen compound and the Diorganosiloxy groups of the cyclic siloxane easily mutually due to their high reactivity exchange and extensively either themselves with the free hydroxyl groups in the silicon di- Qxyd connect or these free hydroxyl groups in otherwise inaccessible. It is believed that the method according to the invention Hydroxylamine acts as a catalyst for the silyl nitrogen compound making this compound very strong activated so that the triorganosiloxy groups are the free Easily substitute hydroxyl groups in silica or otherwise make it inaccessible. Unexpectedly it has now been found that the

ίο silyl nitrogen compound when combined with the other treating agents is used, the cyclic siloxane catalyzes, so that its diorganosiloxy units are very reactive and in extensively most of the free hydroxyl groups of the silicon dioxide starting material which do not reach the SiIyI nitrogen units, substitute or otherwise inaccessible. If only the hydroxylamine and the silyl nitrogen compound are used one, then none is obtained in such an advantageous manner treated filler, as according to the method according to the invention. Even the use of the hydroxylamine alone with the cyclic siloxane does not lead to a filler comparable to the filler obtainable according to the invention. It is therefore in the invention it has been recognized that merely the combination of the three The above-mentioned additives in the stated amounts lead to a composition which is very reactive Diorganosiloxy units from the cyclic siloxane and triorganosiloxy units from the silyl nitrogen having connection that is easy and comprehensive to the free Substitute or otherwise inaccessible hydroxyl groups of the silica starting material, see above that a silica filler is obtained which is not hygroscopic and when it is incorporated into Silicone rubber compositions, be they either thermosetting or cold setting, one long one Maintains storage stability and low viscosity in the uncured state and improved physical properties in the cured state.

The radicals R ² , R ³ and R ⁴ are each hydrogen, a monovalent hydrocarbon radical or a halogen-substituted monovalent hydrocarbon radical. The radicals mentioned can therefore be mononuclear or binuclear aryl radicals, such as phenyl, ToIyI, XyIyI, Naphthyl, etc., halogen-substituted mononuclear or binuclear aryl radicals such as chlorophenyl, chloronaphthyl etc., aralkyl radicals in which the aryl radical is mononuclear and the alkyl radicals I have to 8 carbon atoms, such as Benzyl, phenylethyl etc., lower alkyl radicals with I to 8

such carbon atoms as methyl, ethyl, propyl, butyl, Peiityl, hexyl, octyl, etc., lower alkenyl radicals with 2 to 8 carbon atoms, such as vinyl, allyl, 1-Property I, halogen-substituted lower alkyl radicals having 1 to 8 carbon atoms, such as chloropropyl, trifluoropropyl and cycloalkyl groups such as cyclobutyl, cydopentyl and cyclohexyl.

The radical R ¹ can not be any of the abovementioned monovalent hydrocarbon radicals or halogen-substituted monovalent hydrocarbon radicals but be hydrogen. In addition, each of the radicals R ¹ , R ¹ , R ³ and R ^{4 can be} a mixture of the above-mentioned organic radicals.

The radicals R ¹ , R ² , R ^J and R ⁴ are preferred, in each case lower alkyl radicals having 1 to 8 carbon atoms, such as

Methyl, ethyl or mononuclear aryl radicals such as phenyl. ^{R 1} , R ² , R 'and R ⁴ are even more preferably lower alkyl radicals having 1 to 8 carbon atoms. The hydroxylamines used are known. These

■ J *.

Type of compound must have a hydroxyl group attached to nitrogen. One of the radicals R 'and R ² further bonded to nitrogen can be hydrogen, but both are preferably each monovalent hydrocarbon radicals or halogen-substituted monovalent hydrocarbon radicals,

The cyclic siloxanes used are also described, for example in US Pat. No. 2,938,009.

The tetrasiloxanes used are also known Compounds and they as well as their production are described in the aforementioned PS.

Both types of cyclic siloxanes are produced by hydrolyzing hydrocarbon-substituted chlorosilanes, and the resulting hydrolyzate is cracked or at an elevated temperature in the presence of a catalyst such as potassium hydroxide thermally distilled to remove the cyclic polysiloxanes and distill off. The by thermal Cracking produced cyclic polysiloxanes are mostly tricyclosiloxanes and tetracyclosiloxanes. These different types of cyclic siloxanes just get through Distillation and other known separation processes can be separated from one another. The preferred cyclic The siloxane in the process according to the invention is the tricyclosiloxane, since it is in the process according to the invention Process shows the greatest reactivity and leads to the greatest substitution of the free hydroxyl groups of the silicon dioxide by diorganosiloxy groups Although also the use of the tetracyclosiloxane in the method according to the present invention at one treated filler, which can be useful for many silicone rubber products, is in the am most preferred type of treated filler for making silicone rubber compositions having excellent physical properties to use the tricyclosiloxane in the cured state in the process according to the invention.

The other component in the process according to the invention is the SÜyl nitrogen compound. As already mentioned, only up to 33 mol% of the radicals R «in the molecule may be hydrogen atoms; the remainder should be selected from the above-mentioned monovalent hydrocarbon radicals and halogen-substituted monovalent hydrocarbon radicals. Preferably, however, all R ⁴ - & estes are selected from monovalent hydrocarbon radicals and halogen-substituted monovalent hydrocarbon radicals, in particular from lower alkyl radicals having 1 to 8 carbon atoms.

The silyl nitrogen compound can be a silazane, an aminoxy silicone compound or a silicone amine compound. In the most preferred embodiment of the process according to the invention, a silazane compound in which a is 2 is used. In this most preferred embodiment, therefore, X is

—N—

The aminoxy compound and the amine compound can therefore be used as a silyl nitrogen compound in the Process according to the invention are used, but then not the most preferred embodiment of the e; inventive method. the is the most reactive type of silyl nitrogen compound as a treatment agent in the process according to the invention a silazane. While using the aminoxy compounds and the amine compound according to Uem Although the method according to the invention is a treated Filler is obtained which is useful for many purposes when in silicone rubber compositions is incorporated, which are intended for the manufacture of certain silicone rubber products, is obtained Yet the most beneficial properties when you have a treated filler using one Silazans uses.

ίο The most preferred is hydroxylamine Diethyl hydroxylamine. The most preferred cyclic siloxane is hexamethylicyclotrisiloxane and the like the most preferred silyl nitrogen compound is hexamethyldisilazane.

The hydroxylamine treating agent is in a Concentration of 1/2 to 5 parts, based on 1OG Parts of the silica starting material used. A smaller amount than Vz part does not result in the desired catalytic effect on the others Treatment agent and an amount greater than 5 parts found not to be useful. Most preferred for this hydroxylamine treating agent is an amount of 2 to 3 parts based on 100 parts of the silicon dioxide filler.

The cyclic siloxane is in a concentration of 2 to 25 parts, based on 100 parts of the Silica starting material used. There are both all parts specified so far as well as the following, including the examples, parts by weight.

Less than 2 parts of the cyclic siloxane will not properly treat the filler; h., it a sufficient amount of diorganosiloxy groups is not attached to the hydroxyl groups of the silicon dioxide filler. More than 25 parts of the cyclic Siloxanes do not give any noticeable improvement in the treatment of the filler. Preferably the cyclic siloxanes in the process according to the invention in a concentration of 5 to 14 parts and most preferably from 8 to 9 parts per 100 parts of the

Silica starting material used.

The silyl nitrogen compound is used in a concentration of 1 to 20 parts based on 100 parts of the Silica raw material, used sets if you take less than 1 part of this, you get no acceptably treated filler. The use of more than 20 parts of this compound leads to no further improvement in the treated filler. Preferably the silyl nitrogen compound is im method according to the invention in one concentration

so from 7 to 15 parts and most preferably in one Concentration of 12 to 13 parts used.

In the most preferred silyl nitrogen compound, where X is the meaning

—N—

Y is preferably hydrogen or a lower f, o alkyl radical, such as. B. methyl. The SilyI = nitrogen compound = fertilize are known and z. B. in US Pat. No. 3,635,74 J.

The process of the invention can be used to improve the filler properties of any type of silica starting material and am most preferred is the use of condensed (i.e. obtained by vapor phase oxidation) Silica or precipitated silica or

a mixture of these two starting materials. The method according to the invention for treating a mixture of 5 to 95% by weight of condensed silicon dioxide with a surface area of 50 to 500 m ² / g and 5 to 95% by weight of a precipitated silicon dioxide filler with a surface area of 100 to 500 m ² / g can be used. Although the above mixture of condensed silica and precipitated silica is the most preferred mixture for certain silicone rubber compositions, precipitated silica alone or condensed silica alone or any mixture of these two silicas or other types of silicas can also be treated by the process of the invention. In the process according to the invention, such silicon dioxide AüägärigSiTiäieriäiicri cingcSctZi, uic ciiic Ouci will have an area of at least 50 m ² / g. The condensed silica, which is a fumed silica filler, or the precipitated silica can be produced by any known method and treated in a manner according to the invention.

Another necessary condition for the process according to the invention is the presence of a certain amount of free hydroxyl groups or absorbed water in the silica starting material to be treated or the mixture of starting materials. There must be at least 0.2% by weight of free hydroxyl groups and / or water in the starting material. It is necessary. that at least this small amount of free hydroxyl groups is present in the silicon dioxide starting material so that the filler has the correct properties, ie is in the form of a free-flowing powder and that the various treatment agents can also act. On the other hand, no more than 2% by weight of hydroxyl groups and / or water, based on the weight of the silica starting material, should be present. If more than this amount of hydroxyl groups and / or water is present in the filler, then the free hydroxyl groups and the absorbed water in the filler affect the treatment conversion and the reactivity of the SiIyI nitrogen compound as it binds to the free hydroxyl groups on the silica particles. If the SiO2 starting material contains too little water, a small amount of water can be added to this S1O2. On the other hand, does the S1O2-AUS-starting material have a 7. » high water content, then the water can be removed by heating while at the same time passing a stream of inert gas, such as nitrogen, over the heated SiO particles.

The critical part of the present invention is that the silicon dioxide starting material with the surface and hydroxyl group content defined above at the same time with the correct concentrations of the hydroxylamine, the cyclic siloxane and the Silyl nitrogen compound is brought into contact. Get one of the agents, like the hydroxylamine, first used and the other two agents used in a second stage to treat the filler, then a filler which has not been treated so well is obtained (cf. Examples 1 to 5). It was therefore found that the treated filler which can be prepared by the process of US Pat. No. 3,635,743 is better is than the treated fillers which can be produced beforehand, but that by the treatment process according to the invention an even better treated filler is obtained. Neither do you get such a good one treated filler, as according to the invention, when using hydroxylamine, cyclic siloxane and silyl nitrogen compound used in three consecutive separate stages to treat the filler.

The treatment is carried out for one to eight hours at a temperature in the range from 100 to 180 ^° C., and during this time the filler is constantly stirred. However, stirring is not necessary, just preferred. A more preferred range for carrying out the treatment according to the invention is between 135 and 180 ^° C. The vessel in which the treatment according to the invention of the filler is carried out should be properly sealed. Therefore, a higher pressure will develop in the vessel during the treatment. However, it can be used üüci'i cii'i UueisCiiuu tier BeiiaiiuiuiigMiiiiiei and the treatment can be carried out essentially at atmospheric pressure, for which the vessel is sealed, but excess gases are occasionally vented. However, such an approach is not preferred because it leads to a waste of material. In addition, the reaction rate is accelerated by an increased pressure. The treatment is therefore preferably carried out in a pressure vessel in which a pressure of 0.7 to 7 atmospheres is maintained. In the most preferred embodiment of the invention, the treatment of the filler with the three treatment agents is carried out at a temperature in the range from 145 to 155 "C for three to five hours with stirring. During the process, samples of the filler can be removed from the reaction vessel and can be tested by the aminoxy structure test described below: If the proper flow properties are obtained in this test, the treatment can be stopped, but if one does not want to periodically follow the progress of the reaction, the treatment can be left on for a full 8 hours or more let react with the filler and then the filler is safely treated well enough to meet the criterion of the aminoxy structure test.

After the treatment is finished, the vessel is opened and the remaining amounts of treatment agent, that may still be in the vessel are heated by heating the vessel to a temperature in Range from 150 to 200 ° C, and preferably to 185 to 200 ° C, removed by stripping. It is desirable to remove all nitrogen compounds from the by this stripping Remove filler, d. H. the hydroxylamine and the silyl nitrogen compound. Towards the end of the stripping the filler is examined by acid titration and the stripping is ended when only 50 ppm (parts Nitrogen per million parts of the filler) nitrogen is present in the filler. Is more nitrogen in In the form of a silyl nitrogen compound present in the filler, this nitrogen, be it in the form of the silyl compound present or not, the Properties of the silicone rubber composition into which the filler is incorporated, in undesirable Influence way. In addition, the silicone rubber composition is preserved an undesirable color due to the incorporation of such a filler.

A typical method within the scope of the present invention begins by examining a too SiOr starting material to be treated on the water content. It turns out that water is required

add water and SiO2 starting material to a vessel and heat both to a temperature of 100 to HO ⁰ _{C while stirring the SiO 2.} If the SiO2 starting material contains too much water, then ! yean such excess water at the aforementioned temperature can be removed simply by passing a stream of an inert gas through the vessel in which this S1O2 is located. Thereafter, at the temperature of 11O ⁰ C is added the solution of the three treatment agents in the concentrations indicated above in the reaction vessel and tightly closes this. The vessel is then heated to 145 to 155 ° C., the pressure in the vessel increasing to approximately 1.4 atmospheres to around 3.5 atmospheres, and the vessel is then held in the aforementioned temperature range for a period of 3 to 5 hours Vcr, "j"5'.veisc * .the silica filler is stirred during this time. At the end of this time or in between after the first two hours of the treatment, samples of the filler are taken and the filler is subjected to the aminoxy structure test. If it is found that a flow of about 10 cm occurs in less than 35 seconds, then this shows that the filler has been treated in the best possible way and the treatment can be discontinued. Of course, the filler can also be treated less well than up to the maximum possible point and this less good point can be determined by periodic sampling and determination according to the aminoxy structure test.

After the treated filler has passed the aminoxy structure test, the vessel is opened and the contents are heated to a temperature of preferably 185 ° C., as a result of which the excess treatment agents are removed from the filler. The filler is then examined for nitrogen content, and when the nitrogen content is as low as mentioned above, the filler can be used as an excellent additive for various kinds of silicone rubber compositions. It was found that the fillers treated according to the invention, after their incorporation into cold-curing silicone rubber compositions, imparted these storage times of two years, compared with 3 to 4 weeks or up to 4 months which were possible with fillers treated in a known manner. In addition, it was found that a filler treated in accordance with the invention when incorporated into a low-viscosity polysiloxane containing end groups of silanols does not disadvantageously increase the viscosity of this material and that, in addition, the composition obtained has the desired flow properties and impression properties are used in large amounts and its use results in cured silicone rubber compositions having improved physical properties such as tensile strength, elongation and tear behavior. In addition, it has been found that the filler treated according to the invention does not crosslink with the catalysts and common crosslinking agents used in cold setting and thermosetting silicone rubber compositions. Finally, the low viscosity of such silicone rubber compositions allows them to be easily handled and used Also, do not require special treatment to remove air bubbles from the mixture prior to curing.

The process of the present invention provides a uniquely treated filler; H. a Filler containing 4 to 20% by weight, based on the weight of the filler, of chemically bonded hydrogen diorganosiloxy ortriorganosiloxy units of the formula

and 2 to 10% by weight of chemically bonded hydrogenorganosiloxy or diorganosiloxy units of the formula

contains, where R ⁴ and R ^{J have} the abovementioned meaning.

The treated fillers obtained by the process according to the invention were according to the aminoxy-

Qfriiktnrfract with Citllc (r> ff <=> n \ tf * rCtItC ¹ Vt ** η f \\ f * in V \ & \ ranntf * r

Had been treated wisely. In this test, the treated filler is mixed with a silanol-terminated dimethylpolysiloxane oil having a viscosity of 2500 to 3500 centipoise at 25 ° C which has aminoxy curing agents incorporated therein, such as
1,3,5,7,7-pentamethyl-1,3,5-tris (diethyl-aminoxy)

cyclotetrasiloxane and
1,3,5,5,7,7-hexamethyl-1,3-bis (diethyl-aminoxy)

cyclotetrasiloxane.

There were 16 parts of the latter curing agent used per 1 part of the hardening agent mentioned first. This aminoxy curing agent is a very rapid curing agent that instantly cures the silanol-terminated dimethylpolysiloxane begins. To 16 parts of the silanol-terminated dimethylpolysiloxane oil was added 0.05 Parts of the aminoxy curing agent and 2.5 parts of the treated filler. These ingredients were mixed 1 to 2 minutes by hand and then placed a portion of the mixture on a Boeing flow device which measured the flow properties of the mixture. In this device the mixture was in the tray and then the horizontal test device was taken and placed on one end arranged so that the polysiloxane could flow vertically down from the tray on a scale. the The amount of downward flow due to gravity after 35 seconds is measured in cm des River.

The invention is explained in more detail below with the aid of examples. The surfaces of the inserted Silica starting material had - as explained at the beginning - been determined according to BET.

example 1

There were 90 parts of condensed silicon dioxide with a surface area of 200 ^{m 2} / g and 10 parts of precipitated silicon dioxide with a surface area of 7 ^1/2 m 2 / g with a total moisture content which was adjusted to 0.5 to 1% by weight, to 145 to Heated 170 ° C and then a solution of 2 parts of diethylhydroxylamine, 12 parts of hexamethyldisilazane and 8 parts of hexamethylcyclopolysiloxane added and the whole sealed and heated for 6 hours Thereafter, the volatile materials were removed at a temperature of 160 ° C to a nitrogen content of less than 50 ppm. A sample of the treated filler was then tested in the aminoxy structure test and it flowed 10 cm in 15 seconds on a Boeing tester.

Example 2

90 parts of condensed silicon dioxide with a surface area of 200 m ² / g were heated to 250 to 270 ^° C. and then 18 parts of hexamethylcyclopolysiloxane were added. The mixture was heated for an additional 3 hours. The volatile materials were then removed from the filler. The mixture was cooled to 145 to 170 ^° C. and 10 parts of precipitated silicon dioxide with a surface area of approximately 275 m ² / g were then added, the entire mixture having a moisture content of 0.5 to 1% by weight. To this mixture were added 20 parts of hexamethyldisilazane and 2 parts of diethylhydroxylamine. The mixture was heated for 6 hours in a sealed vessel to a temperature of 140 to 170 ^° C. The volatile material was then removed

HACtanHtpilf »alle Af * r Micr» hiin <r Kic vn <* in <»m QtioUctoff-

^^^ * u * «· · m ^ l · w · λ ^% m ^ *» * ** W · λ ψ a ϊ »* ^ · 9 λ τ · IjB -] r tir n ΐτ \ ji ■ · ^ * · · Ϊ ^ j \ i w · * w \ ^m ~ ■ ■

content less than 50 ppm. The treated filler exhibited a flow of about in the aminoxy structure test 2.5 cm in 120 seconds.

Example 3

90 parts of condensed silicon dioxide with a surface area of 20OmVg and 10 parts of precipitated silicon dioxide with a surface area of approximately 275 m ² / g and a set total moisture content of 0.5 to 1% by weight were used. This mixture was heated to 145-170 ⁰ C. was then added to the mixture 2 parts diethylhydroxylamine added and heated for 6 hours in a sealed vessel. The volatile constituents were then removed to a total nitrogen content of less than 50 ppm. Then 8 parts of hexamethylcyclotripolysiloxane were added and ^{the mixture was again heated to 145 to 170 °} C. for 6 hours. The volatile constituents were then also removed from the mixture. Finally, 12 parts of hexamethyldisilazane were added to the filler mixture at a temperature of 145 to 170 ^° C. and the mixture was heated in a sealed vessel for a further 6 hours. The volatiles were then removed from the filler again until the total nitrogen content was less than 50 ppm. The product obtained showed a flow of 10 cm in 180 seconds in the Äminoxy structure test.

Example 4

90 parts of condensed silicon dioxide with a surface area of 20OmVg and 10 parts of precipitated silicon dioxide with a surface area of 275 m ² / g and a total moisture content of 0.5 to 1% by weight were used. This mixture was heated to 145 to 170 ⁰ C, and then were added 2 parts diethylhydroxylamine and the mixture was heated for another 6 hours. Thereafter

K) the volatile constituents were removed from the filler up to a total nitrogen content of less than 50 ppm. A solution of 8 parts of hexamethyltricyclopolysiloxane and 12 parts of hexamethyldisilazane was then added and the mixture was heated in a sealed vessel to a temperature of 145 to 170 ^° C. for 6 hours

Hii ^ cpr 7 r * \ tf * nift * rntf * pi ^ n YT! ^^ ΓΏ pHJjctrtff rli «*

volatile constituents up to a total nitrogen content of less than 50 ppm. The thus obtained In the aminoxy structure test, filler had a flow of 10 cm in 168 seconds.

Example 5

90 parts of condensed silicon dioxide with a surface area of about 200 m ² / g and 10 parts of precipitated silicon dioxide with a surface area of 275 mVg and a set total moisture content of 0.5 to 1.0% by weight were used. the

jo filler is heated to 145 to 170 ⁰ C, and then you were added 2 parts diethylhydroxylamine and 8 parts of hexamethylcyclotrisiloxane. Thereafter, the mixture thus obtained was heated for 6 hours in a sealed vessel at 145 to 17O ⁰ C. Thereafter,

j5 the volatile constituents were removed from the filler to a nitrogen content of less than 50 ppm. Thereafter, 12 parts of hexamethyldisilazane were added to the filler mixture and the mixture was again heated to 145 to 170 ^° C. for 6 hours -Structure test showed a flow of 10 cm in 31 seconds.

Claims (3)

Claims; I. A method for improving the filler properties of particulate silicon dioxide, in which a Silica starting material with a surface area of at least 20 mVg and a content of 0.2 to 2% by weight of hydroxyl groups and / or Water at elevated temperatures with a hydroxylamine, a silyl nitrogen compound and a cyclic siloxane is treated thereby characterized in that! 00 parts of the silica starting material at a temperature from 100 to 180 ° C at the same time i) ¹ I ₁ to 5 parts of a hydroxylamine of the formula R ² R ¹ -N-OH ii) 2 to 25 parts of a cyclic siloxane of formula (RfSiO) ₃ and iii) 1 to 20 parts of a silyl nitrogen compound of the formula are treated, where R ^{1 is} a monovalent hydrocarbon radical or a halogen-substituted hydrocarbon radical, R ² , R ³ and R ^{4 are} each hydrogen, a monovalent hydrocarbon radical or a halogen-substituted monovalent hydrocarbon radical, with R ³ and R ^{4 being} a maximum of only 33 mol% hydrogen may, a has the value 1 or 2, and X -NR ⁵ Y, - ONR | or - N— denotes, where R ⁹ denotes a monovalent hydrocarbon radical or a halogen-substituted monovalent hydrocarbon radical and Y denotes hydrogen or R ⁵ . 2. The method according to claim 1, characterized in that the treatment agent 3 to 8 hours be brought into contact with the filler for a long time. 3. The method according to claim I or 2, characterized in that R ¹ , R ² , R ³ and R ^{4 are} each an A Iky! Group. The present invention relates to a method for improving the filler property of finely divided silica, in which a silica starting material with a surface area of at least 20 mVg and a content of 0.2 to 2% by weight of hydroxyl groups and / or water at elevated temperatures a hydroxylamine, a silyl nitrogen compound and a cyclic siloxane. (This one The surface values used relate - as in the case of the characterization customary according to the state of the art for finely divided silicon dioxide - to data obtained according to the BET measurement technique by means of nitrogen adsorption; see e.g. US-PS 30 24 126 _r ) A method of the aforementioned type is described in DE-OS 20 00 461. According to this DE-OS, the filler must contain ammonia or an ammonia derivative, such as a hydroxylamine ίο pretreated and then treated with a silyl nitrogen compound and a cyclic siloxane will. According to this method, the filler can also be used before or after pretreatment with ammonia or an ammonia derivative with a cyclic alkyl po- % lysiloxane are treated. In this method, the filler is treated one after the other in a certain order with different treatment agents. The filler must first be treated with ammonia or an ammonia derivative, then can the filler may optionally be treated with a cyclic alkylpolysiloxane and finally will he treated with a silyl nitrogen compound This process therefore requires that the filler only with ammonia or one Ammonia derivative is treated and then in a second and subsequent stage the filler is treated with a silyl nitrogen compound, which can be a silazane. In this DE-OS it is expressly pointed out that one with the ίο the procedures described there, associated advantages can only be obtained if the treatment soaps are carried out separately and independently of one another will. This method was advantageous in that it contained a greater proportion of bound or Γ) free bound by triorganosiloxy groups Led hydroxyl groups so that the filler was treated well. You worked such a filler in Silicone rubber compositions, a cured product was obtained with an opposite of previous ones Products improved physical properties. Although according to the procedure of this DEOS treated filler obtained was useful for some purposes in silicone gum compositions, showed the corresponding compositions each but not yet of sufficient storage stability speed and they also had undesirably high viscosities in the uncured state. The invention was therefore based on the object of creating a method of the type mentioned at the beginning the silica fillers obtained which in the silicone compositions in which they are incorporated do not have the disadvantages of the defective Cause storage stability and high viscosity in the uncured state, «According to the invention, this object was achieved in that 100 parts of the silicon dioxide starting material at a temperature of 100 to 180.degree at the same time with